powershell-sort-array-of-objects

powershell-sort-array-of-objects.md

# pwsh
PowerShell 6.2.1
Copyright (c) Microsoft Corporation. All rights reserved.

https://aka.ms/pscore6-docs
Type 'help' to get help.

PS /root/mnt> class A {                                        
>> 
>> 
>>     [string] $x
>> 
>>     A ([string] $x) {
>>         $this.x = $x
>>     }
>> 
>>     [Boolean] Equals([A] $other) {
>>         if ($this.x -eq $other.x) { return $true } else { return $false }
>>     }
>> 
>> }
>> 
>> 
An error occurred while creating the pipeline.
+ CategoryInfo          : NotSpecified: (:) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : RuntimeException
 
PS /root/mnt> $error[0].Exception.GetBaseException() | select *
You cannot call a method on a null-valued expression.
At line:1 char:1
+ $error[0].Exception.GetBaseException() | select *
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull

PS /root/mnt> class A {
>> 
>>     [string] $x
>> 
>>     A ([string] $x) {
>>         $this.x = $x
>>     }
>> 
>>     [Boolean] Equals($other) {
>>         if ($this.x -eq $other.x) { return $true } else { return $false }
>>     }
>> 
>> }
>> 
>> 
PS /root/mnt> $x1 = [A]::new('xxx'); $x2 = [A]::new('yyy'); $x3 = [A]::new('xxx'); $x4 = [A]::new('zzz')
PS /root/mnt> $a = @($x1, $x2, $x3, $x4)
PS /root/mnt> $a | ForEach-Object { Write-Host $_.x }
xxx
yyy
xxx
zzz
PS /root/mnt> $a_cleaned = @($a | select -Unique)
PS /root/mnt> $a_cleaned | ForEach-Object { Write-Host $_.x }
xxx
PS /root/mnt>

class A : System.IComparable {

    [string] $x

    A ([string] $x) {
        $this.x = $x
    }

    [int] CompareTo($other) {
        return $this.x.CompareTo($other.x)
    }

    [Boolean] Equals($other) {
        if ($this.x -eq $other.x) { return $true } else { return $false }
    }

}


$x1 = [A]::new('xxx'); $x2 = [A]::new('yyy'); $x3 = [A]::new('xxx'); $x4 = [A]::new('zzz')
$a = @($x1, $x2, $x3, $x4)
$a | ForEach-Object { Write-Host $_.x }
write-host "--"
$a_cleaned = @($a | select -Unique)                                                                                   
$a_cleaned | ForEach-Object { Write-Host $_.x }

It works via the CompareTo() method in the class and it seems that Equals() method is not used at all by select -Unique.

It works with Sort-Object -Unique too where duplicated objects are remove and the array is sorted.